Fixed issues with assertions about ftype and rad.

The pull request fixes issues https://github.com/vtsuperdarn/davitpy/issues/51 and https://github.com/vtsuperdarn/davitpy/issues/52. fetchUtils code is now more general and allows for remote and local fetching of .map or .mapex files.

Another change to make note of is that the rad argument is an optional argument. I have already made the necessary changes to the feature_use_fetchUtils branch (see pull request in @jspaleta's fork here https://github.com/jspaleta/davitpy/pull/3) so that it is compatible with this pull request.

Also this pull request includes updated documentation and an implemented __name__==__main__ test that automatically attempts to retrieve files fitex and mapex files from the VT server and fitacf and map files from the usask server. The test allows one to check for expected behaviour.

@mrwessel, could you test this code out since you were the one who found the bugs?